Who has tested transistors with different gain? I wonder if 2n5088 with hfe close to 600 or bc547b with hfe around 350 would be better?I had forgotten this project, but today I found a layout and a half populated board. So, after three years, this will be finished soon.

Built it this afternoon. I like the general tone, more overdrivey and less all-out fuzz. With 1µ the Fat control isn't doing that much for me, but I think that is due to the tone control, which cuts a lot of bass in general. I think I would have preferred a BMP style control or a simple treble cut here. Transistors are all BC550C. I'll also try a bigger feedback resistor for higher maximum gain, right now it's just a little bit lacking.

After three years, I finally finished my build...- Using bc547b transistors with hfe around 350 is no problem, I even liked them better than 2n5088 with higher gain- I tried both variants of the tone circuit that were discussed in this thread. Both are useful, so I put them on a switch as shown in the vero board layout.

Wiring five 9mm pcb-mount pots in a 1590b enclosure is slave labor! Does anybody sell a pcb for this circuit?

...but the bias isn't perfect in my build. Maybe I'll use transistors with higher hfe or increase the feedback resistor?The original pedals sounds thicker and creamier in some of the videos.

And I have a strange problem with hiss in my pedal:- hiss increases, if I turn up the bias pot, but after the 2 o'clock position, it's totally gone. Maybe this is normal, because that's the point where the sound gets gated.- there's hiss on the fat pot, but only at two small areas, around 10 o'clock and 2 o'clock, and only if the fuzz put is fully clockwise. Maybe caused by creeping current on the veroboard? I used some foam as isolation, that I've never used before...

Some people here and at tagboardeffects reported problems with hiss, oscillation, touch sensitive parts and some power adapers...All of that might be caused by the fat pot, which is definitely wired wrong in the existing schematics and layouts. It should look like this:

Scarab Deluxe Fat .jpg

Quick fix: Add a jumper between lugs 2&3 of the pot or on the board. The pot is still wired backwards, but that doesn't matter as it's linear taper.

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Came across this schematic through a google image search. The two differences I noticed are the 22uf cap coming off the wiper of the Fuzz pot and the extra resistor and cap to ground on the tone control. Is this a version 2 by Basic Audio? Or just someone modding the original design?

~arph wrote:Yes, you can influence taper, but shouldn't the 10k be connected to the wiper instead of the low side of the pot to simulate a reverse log action? The way it's connected now just makes the 50kB pot a 8.3kB pot.

I think the tone pot probably needs to have pins 2 and 3 joined. That makes the 10k in parallel with the pot a true 0-8.3k C-taper variable resistor, and it makes the tone control a true shelf control with the 100n in series with varying resistance from 10.5k to 2.2k.